Flow cytometry has become an indispensable tool for numerous areas of biological and medical research. Multiple parameters can be measured simultaneously on individual living cells with such a speed that an entire population of cells can be analyzed within seconds to minutes. Rare and unusual events are identified rapidly and expression levels of defined cell-surface or intracellular molecules can be quantified with great ease and precision. The ability to detect such events is particularly critical for the study of cancer and immunological diseases. Uses of the flow cytometry instrument include the monitoring of knockout mice and their reconstitution, analysis of TCR-transgenic mice, the tracking of transferred lymphoid subpopulations, quantification of EGFP-labeled fusion proteins, MHC-tetramer analyses of T cells, identification of variant bacteria, etc. The need for flow cytometric analyses has markedly increased because of an increased awareness of the diverse applications of multiparameter flow cytometry resulting in highly limited availability of the instruments. The PI and the Technical Director have a combined 40-year work experience in analytical cytology. A new 3 Laser BD Digital LSR TM will drastically reduce the current waiting times and provide a cost-efficient highly informative rapid method of analysis to a diverse group of NIH-supported scientists. The Laser BD Digital LSR TM is a state-of-the-art, triple laser, 10 parameter, 8-color analyzer, with a dual thresholding ability ideal for analysis of small particles. The efficiency of the usage of the Laser BD Digital LSR TM will be further increased by placing the unit into the existing Flow Cytometry Facility. Integration of this unit into this facility will guarantee supervision and management by an outstanding, highly experienced Technical Director, Julie Auger, and continued support as part of the institution's Cancer Center Core. Inclusion into an already established system of on-line bookings ensures and documents the maximal and fair usage of the instrument. An already established Internal Advisory Committee will oversee an equitable and appropriate use by a broad multidisciplinary group of scientists while giving priority to NIH supported groups.